1. Introduction
Recycling has become a key issue in waste management. In fact, the globally produced waste presently amounts to 2 billion tons/year and, given the continuous population growth and increase in industrial development, it is expected to reach 3.40 billion tons/year by 2050
[1][2]. Considering that the organic fraction represents approximately 45% of the total waste and that it is rich in nutrients and biochemicals, its recycling is certainly of great relevance from a circular economy perspective.
In the past, organic waste was mainly disposed of in landfills with the now well-known environmental impacts
[3]; alternatively, it was reused as food for animals or directly applied on agricultural lands as fertilizer. More recently, it has been recognized that organic waste can be used as feedstock for platform chemicals
[4][5][6][7]. Among the techniques suggested for the conversion of organic waste into valuable products, biological treatments for the production of energy (e.g., biogas from anaerobic digestion) and organic soil improvers or fertilizers (compost from aerobic composting and digestate from anaerobic digestion) are those most commonly used
[5][8]. In the case of application to soil, important features of the product are its stability and maturity, the former indicating low biological activity and high resistance to decomposition, the latter referring to the stabilization of the physicochemical characteristics of the material, the disappearance of phytotoxicity, and the ability to favor seed germination and plant growth
[9][10].
Given its ease of implementation and low operational costs, the most commonly used organic waste treatment is composting
[11]. Composting is the decomposition process of organic matter (OM) performed in aerobic conditions by microorganisms
[12], which allows the transformation of organic wastes of different kinds, both vegetal and animal, into a stable organic substance rich in “humus”. Humus is constituted by the high molecular weight association of amphiphilic compounds, rich in carboxylic groups, slow to decompose under natural conditions, and is responsible for many physicochemical properties that ensure soil fertility. The composting process is naturally driven by microorganisms, which use OM and oxygen for their metabolism, producing heat, CO
2, H
2O, minerals and stable OM
[13]. This process starts with a bio-oxidative phase characterized by a rising temperature, which reaches 45–70 °C. During this phase, which lasts for days, thermophilic microorganisms decompose OM very fast, using the most easily available substances. The high temperature ensures sanitation, i.e., the inactivation of most pathogens and invasive plant seeds. Afterwards, the temperature progressively decreases to mesophilic conditions, and the fresh compost enters a curing phase, which can last for weeks, in which decomposition continues, involving the more recalcitrant compounds (such as lignin) and bringing to the formation of humic compounds (fulvic and humic acids, and humin) with high maturity and stability. Compost has great value as a soil amendment and fertilizer, with applications in agriculture, horticulture, and gardening, and hence represents a perfect example of a circular economy; in fact, the last decades have seen an increase in compost production. Today, in Europe 42 million tons of waste per annum, that is 59% of the separately collected biowaste, both municipal and commercial/industrial, is composted
Understanding the transformations of OM that take place during the composting process is fundamental for the agricultural application of the stabilized waste and for the optimization of process parameters, also considering that national and international regulations have established stringent requirements for the use of this product as fertilizer or soil amendment in terms of organic carbon content, humic substance content, etc. For these reasons, since the 1990s, many studies have been published in the scientific literature testing and comparing different chemical and instrumental methods for assessing compost stability and/or maturity, as, for example, measurement of pH, electrical conductivity, CO
2 evolution rate, seed germination rate, dissolved organic carbon, volatile organic carbon, C/N ratio, and humic acid content (see for instance
[15][16][17][18][19][20][21]). To this end, besides conventional analytical methods, advanced instrumental techniques, such as thermal analyses, Fourier transform infrared spectroscopy (FTIR), UV–Vis and fluorescence spectroscopies, nuclear magnetic resonance (NMR) spectroscopy, gas chromatography–mass spectrometry, and scanning electron microscopy, can be used to assess the stabilization of organic matter and the quality of the final product. In fact, these techniques provide detailed information on compositional, functional, and behavioral properties of organic materials, even complex ones such as compost. Nevertheless, it is generally agreed that a combination of analyses is advised for a thorough characterization.
Among the techniques that can give access to compositional information of OM, NMR, and solid-state NMR (SSNMR) in particular, stands out as a powerful method to access comprehensive qualitative and quantitative structural information not available from other techniques. Compared to liquid-state NMR, which is useful for studying soluble components, especially those with low molecular weight (see Refs.
[22][23] for a comprehensive review), SSNMR has many advantages when applied to OM: (i) it allows bulk samples to be analyzed without pretreatments or the use of solvents, which may introduce artifacts; (ii) it can be used to investigate insoluble OM samples or fractions; (iii) it allows a much higher sample concentration, enhancing signals and saving instrument time; (iv) it is conservative, i.e., it does not consume sample; (vi) it allows the investigation of anisotropic interactions, averaged out in solution NMR by the fast isotropic tumbling of molecules; (v) it allows domains and heterogeneities to be identified within OM structures. The vast majority of SSNMR studies of OM reported in the literature involve the observation of
13C nuclei, with only a few exploiting
15N and
31P. Indeed,
13C SSNMR yields useful information on OM composition in terms of organic functional groups
[18][24].
2. 13C Solid-State NMR Spectroscopy for the Investigation of Organic Matter in Compost
13C has a natural abundance of 1.11%
[25],[26], which results in a good balance of sensitivity and spectral “simplicity” since complex interactions among
13C nuclei can be neglected. The most important nuclear property used for the identification of functional groups is chemical shielding. On the basis of this property, nuclei in different chemical environments give rise to signals at different resonance frequencies, expressed as chemical shifts. Experimental techniques providing high-resolution
13C SSNMR spectra are at present routinely available on SSNMR instruments, the most important being Magic Angle Spinning (MAS) and high-power decoupling from abundant
1H nuclei. In the most basic experiment, usually called direct polarization MAS or direct excitation MAS (DE-MAS), these techniques are combined with a radiofrequency excitation pulse on
13C. The
13C DE-MAS experiment gives the most accurate quantification of the different species in an OM solid sample, provided that it is performed with a sufficiently long recycle delay between consecutive scans (five times the spin-lattice relaxation time,
T1, of the
13C nuclei). Since
T1 values for
13C nuclei in the solid state can be considerably long (even hundreds of seconds), extremely long measurement times are required for acquiring quantitative
13C DE-MAS spectra with an acceptable signal-to-noise ratio. For this reason
1H-
13C cross polarization MAS (CP-MAS) experiments are most commonly used in the investigation of OM samples. In CP-MAS experiments, the
13C signal is created by magnetization transfer from the abundant
1H nuclei during a time interval called contact time, with an enhancement by up to a factor of four. Moreover, in CP experiments the recycle delay is determined by the longitudinal relaxation of the
1H nuclei, which is usually much faster than that of
13C. This allows recycle delays of a few seconds to be used, with a substantial reduction in the experimental time. It is worth noting that, while CP-MAS is an excellent technique for investigating the qualitative composition of a sample, the relative peak intensities may not be fully preserved. However, it has been reported that in the case of compost
13C CP-MAS NMR spectra recorded with a contact time of about 1 ms and a recycle delay of a few seconds show a similar intensity loss (<10%), with respect to the quantitative spectrum, for signals of all functional groups
[27], allowing these conditions to be used for relative quantitation. This also generally applies in the comparison of a series of spectra of samples with similar composition. Therefore,
13C CP-MAS NMR experiments with a contact time of 1 ms and a recycle delay of a few seconds are usually employed in works on OM in composts to investigate and compare OM composition in the feedstock (biomasses or wastes) and throughout (or only at the end of) the decomposition process.
The spectra are typically analyzed by distinguishing OM carbons from different functional groups on the basis of the chemical shift. Given the complex and heterogeneous chemical nature of OM, spectra span a chemical shift range of over 200 ppm, with a strong overlap of signals. Therefore, spectral regions, rather than individual signals, are usually identified and assigned to specific organic species: (i) the 0–45 ppm spectral region is ascribed to alkyl carbons, with short chain aliphatic carbons from volatile fatty acids and steroid-like molecules resonating between 0 and 28 ppm
[28] and long chain aliphatic carbons from plant aliphatic biopolymers (suberin, cutin, waxes, fatty acids)
[29] and proteins
[30] between 28 and 45 ppm; (ii) O-alkyl and N-alkyl carbon signals, ascribable to lignin, carbohydrates (i.e., cellulose and hemicellulose), and proteins
[31], are observed between 45 and 110 ppm; (iii) the 110–160 spectral region is assigned to aromatic carbons present, for instance, in lignin and polyphenols
[32]; (iv) signals of carboxyl carbons in esters, acids, and amides (160–190 ppm) and carbonyl carbons in aldehydes and ketones (190–220 ppm) are observed between 160 and 220 ppm. It must be noted that slightly different spectral region ranges are indicated in the literature by different authors. Some resolved signals are also assigned to functional groups belonging to specific biomacromolecules present in biomass samples
[33],[34].
Table 1.
Spectral regions used in the analysis of
13
C MAS NMR spectra of OM and assignment to carbons in different functional groups.
Chemical shift range
|
Assignment
|
Conventional region name
|
0-28 ppm
|
CH3 and CH2 in short chain and simple aliphatics
|
Alkyl C
|
28-45 ppm
|
CH2 and CH in long aliphatic chains
|
45-60 ppm
|
O-CH3; CH-N; aliphatic quaternary C
|
O-Alkyl C
|
60-95 ppma
|
C2-C6 in cellulose and hemicellulose; alcohols; ethers
|
95-110 ppmb
|
C1 of cellulose and hemicellulose; anomeric carbon of polysaccharides
|
110-145 ppmc
|
Unsubstituted or alkyl-substituted aromatic C
|
Aromatic C
|
145-160 ppmd
|
O,N-substituted aromatics
|
160-190 ppm
|
Carboxylic acids; esters; amides
|
Carboxyl/carbonyl C
|
190-220 ppm
|
Ketones; aldehydes
|
aalso referred to as O-alkyl C region; balso referred to as di-O-alkyl C region; calso referred to as aryl C region; dalso referred to as O-aryl C region.
Although 13C CP-MAS NMR is semiquantitative, the integral values of different spectral regions (expressed as % of total area) have been extensively used as quantitative proxies for the relative C distribution among major OM functional groups in the feedstocks and in the intermediate/final products, thus monitoring the transformation process of the different components. It must be pointed out that, although most authors do not give errors on the integral intensities and some even report integral values with one or two decimal digits, errors on the units digit are to be expected, deriving from sampling and spectral processing. Moreover, normally, relative integral intensities are compared without taking into account the decrease in the absolute amount of carbon in OM due to decomposition.
Different indices are also used to express OM composition, the most common ones being the Alkyl C/O-Alkyl C (A/OA) ratio, the aromaticity index (ARM), and the hydrophobicity index (HB/HI), generally defined as:



13C SSNMR experiments on OM samples in waste management are generally carried out on spectrometers working at 13C Larmor frequencies of 75-125 MHz, although a frequency of 150 MHz is used in more recent studies and frequencies as low as 25 MHz were employed in the older ones. MAS rotors with diameters of 4 mm, containing few tens of milligrams of sample, and MAS frequencies of 8-13 kHz are usually employed. Few cases are also reported where rotors with 7 mm diameter and spinning rates of 3.5-5 kHz were used. As previously said, 13C CP-MAS experiments are usually performed with a contact time of 1 ms, although cases are reported where longer contact times (2-3 ms) are used. In these experiments, the recycle delay ranges from 0.5 to 5 s and few thousands of scans are acquired.
Before 13C SSNMR experiments, OM samples are simply dried (by freeze-drying, oven-drying at 40-110°C, or air-drying), ground, and possibly sieved to obtain a fine powder; the latter operation is not strictly necessary, but it is useful since it ensures stable sample spinning and, consequently, a better spectral resolution. Considering that only few tens of milligrams of powder are necessary for the analysis, accurate sampling and homogenization are critical to obtain a representative sample.
Several studies on composts, however, instead of investigating the bulk material, focused on extracts. Different types of extracts were investigated, that is, humic substances (HSs), dissolved organic matter (DOM), or compost tea (CT). Humic substances are stable compounds with a complex and variable composition, mainly containing aromatic rings linked by methylenic chains and/or oxygen atoms, with carboxyl and hydroxyl groups bonded to the rings and the alkyl chains. On the basis of their solubility, two different extractable HS fractions can be obtained, i.e. fulvic acids (FAs, soluble at any pH value) and humic acids (HAs, soluble at pH>2). The extraction of HSs is performed mixing the dry compost in an alkaline solution; HAs can then be separated by acidifying to pH 1.0. HAs have higher molecular weight and degree of aromatization with respect to FAs, which, on the other hand, are richer in carboxyl and hydroxyl groups [35]. Thanks to their highly aromatic structure, HAs are stable compounds and their amount is typically considered as a measure of compost maturity [36]. In fact, during composting HAs tend to increase whereas FAs tend to decrease [37]. Compost DOM is a mixture of low-molecular weight compounds, such as sugars and free amino acids, and high-molecular weight compounds, among which also HSs [38]. DOM is a very small fraction of the total organic matter present in compost, decreasing as feedstock stabilization proceeds, but it is an important component since many biochemical transformations that occur during composting take place in solution. DOM is extracted from compost by shaking the material with ultrapure water; DOM can be further divided in a hydrophobic fraction (HoDOM) and a hydrophylic fraction (HiDOM) using the Amberlite® XAD-8 or Supelite™ DAX-8 resin [38]. Finally, compost tea is an aqueous extract obtained from the fermentation of compost in water either in forced aerated or non-aerated conditions [39].
3. 13C Solid-State NMR Applications to Composting
The literature reports many examples of the application of
13C MAS NMR to the investigation of compost, covering a very broad range of diverse feedstocks, including, often mixed, animal (cattle, swine, chicken, buffalo) manure
[40][41][42][43][44][45][46][47][48][49][50][51][52], vegetal residues
[10][41][42][52][53][54][55][56][57][58], grape marc
[50][59], ground coffee and fresh grass
[10][57], cotton gin waste
[45], rice husk, bran or straw and wheat straw
[44][46][56], domestic organic wastes
[55][57][60], and municipal solid wastes (MSW)
[27][61][62]. The composting process has been followed by means of
13C CP-MAS NMR for different times, ranging from a few days, for specifically investigating the initial part of the process
[10], up to more than one year
[46]. An example of the evolution of the
13C CP-MAS spectrum of different feedstocks with composting time is shown in
Figure 1. In most cases the reported experimental data are the integral areas of the characteristic spectral regions described
in Section 2. These data are catalogued in
Table 2, indicating for each study the feedstock and the composting time.
Figure 1. 13C CP-MAS NMR spectra of composts (dashed line) and corresponding feedstocks (solid line). Feedstock compositions are: (
a) exhausted grape marc and cattle manure 76:24 (
w:
w); (
b) grape marc and cattle manure 72:28 (
w:
w); (
c) exhausted grape marc and poultry manure 67:33 (
w:
w). Reproduced from Ref.
[50].
Table 2. Relative areas (% of total area) of the different regions of 13C CP-MAS NMR spectra for compost samples and corresponding feedstocks reported in the literature.
Ref. a |
Feedstock b |
Sample c |
Alkyl C |
O-Alkyl C |
Aromatic C |
Carboxyl/
Carbonyl C |
|
by means of different
13C SSNMR measurements. In this case the decomposition of a bio-degradable starch-based thermoplastic mulching film for horticultural crops was followed in a real on-farm composting process. By recording variable contact time
13C CP-MAS NMR spectra of the film before and after composting, the authors detected changes in the
1H longitudinal relaxation time in the rotating frame,
T1ρ, values that were ascribed to an alteration of the inter-molecular linkages among the organic components of the plastic, due to the progressive decomposition of its constituents.
The effect of specific additives on different composts was also investigated. Skene et al.
[67] studied the decomposition of straw in the presence and absence of inorganic matrices, such as sand, kaolin, and loamy sand, and found that straw incubated in inorganic matrices decomposes faster than straw alone and that sand seems to preserve alkyl groups. Considering that biochar in ruminant diets is being assessed as a method for simultaneously improving animal production and reducing enteric CH
4 emissions, Romero et al.
[40] examined the effects of feeding a pine-based biochar to beef cattle on manure composting.
13C CP-MAS NMR showed that biochar increases compost aromaticity, without altering the bulk C speciation of manure. Liu et al.
[43] investigated the effect of adding biochar to a swine manure compost, and found a promoting influence of biochar on the aromatization process.
13C SSNMR has also been applied to freeze-dried extracts of compost to aid the understanding of the chemical structure of this complex material, as well as the changes occurring in OM during composting. Results on the contribution of the different functional groups to the
13C CP-MAS NMR spectra of different types of extracts obtained from various composts and feedstocks are reported in
Table 3.
Table 3. Relative areas (% of total area) of the different regions of 13C CP-MAS NMR spectra for extracts of composts and corresponding feedstocks reported in the literature.
Ref. a |
Feedstock b |
Sample c |
Alkyl C |
O-Alkyl C |
Aromatic C |
Carboxyl/
Carbonyl C |
|
|
|
CH | 3O/CHN |
O-/Di-O-alkyl C |
Aryl C |
O-Aryl C |
|
|
|
|
|
CH3O/CHN |
O-/Di-O-Alkyl C |
Aryl C |
O-Aryl C |
Carboxyl C |
Carbonyl C |
[41] |
Olive mill waste/orchard pruning residues |
C 200 d |
17.39 |
11.63 |
45.86 |
12.31 |
5.75 |
7.06 |
[72] |
SM/poplar sawdust (5:3 w:w) |
HA 60 d |
30.3 |
33.9 |
16.8 |
7.1 |
11.9 |
Olive mill waste/animal manure/wool residues |
C 200 d |
26.82 |
15.32 |
38.59 |
6.93 |
4.0 |
8.34 |
[52] |
ChM/saw dust (3:1 w:w) |
C 56 d |
28.38 |
32.26 |
16.51 |
|
CM/saw dust (3:1 w:w |
+sepiolite 3 wt% |
HA 60 d |
26.7 |
29.9 |
18.3 |
8.4 |
16.8 |
) |
+sepiolite 6 wt% |
HA 60 d |
34.7 |
22.6 |
17.4 |
7.9 |
17.4 |
C 56 d |
22.13 |
32.20 |
10.49 |
+sepiolite 9 wt% |
HA 60 d |
24.3 |
29.4 |
18.3 |
10.4 |
17.6 |
SM/saw dust (3:1 w:w) |
+sepiolite 12 wt% | C 56 d |
HA 60 d31.62 |
24.0 | 41.36 |
29.917.71 |
20.8 |
8.7 |
16.5 |
Soybean meal/saw dust (3:1 w:w) |
C 56 d |
37.94 |
43.16 |
18.40 |
[69] |
CYN/corn straw and WC (70:30 w:w) |
HS 100 d |
20.93 |
15.98 |
29.78 |
16.26 |
5.51 |
11.54 |
Lemon peel/saw dust (3:1 w:w) |
C 56 d |
36.23 |
41.10 |
17.43 |
COF/corn straw and WC (70:30 w:w) |
HS 100 d |
30.63 |
13.07 |
24.69 |
15.33 |
3.42 |
12.85 |
[58] |
PEP/corn straw and WC (70:30 w: | Wood chips/vegetable R/aromatic plant R |
wC1 |
33.9 |
13.0 |
31.3 |
) |
HS 100 d |
20.06 |
14.2212.6 |
2.1 |
7.2 |
35.75 |
14.40 |
4.49 |
11.08 |
C2 |
38.2 |
12.3 |
26.8 |
11.5 |
2.9 |
8.2 |
[87] |
CYN/WC (70:30 w:w) |
HA 100 d |
22.2 |
13.8 |
27.5 |
20.0 |
5.7 |
10.9 |
C3 |
23.4 |
11.7 |
44.0 |
[ | 12.1 |
3.7 |
5.1 |
43] |
SM/rice straw 4:1 |
HA FS |
46.8 |
19.6 |
18.1 |
15.5 |
C4 |
21.0 |
11.8 |
41.1 |
| 14.3 |
3.8 |
8.1 |
HA 40d |
28.4 |
21.7 |
31.3 |
18.7 |
C5 |
19.0 |
11.4 |
42.4 |
15.5 |
3.8 |
7.9 |
22.2 |
SM/rice straw 8:1 |
HA FS |
45.8 |
17.2 |
14.7 |
22.3 |
C6 |
24.6 |
10.9 |
38.7 |
15.1 |
|
HA 40d |
28.9 | 3.3 |
26.8 | 7.4 |
31.6 |
C7 |
35.7 |
11.8 |
31.0 |
11.8 |
2.5 |
7.2 |
12.7 |
SM/rice straw/biochar 8:1:1 |
HA FS |
43.2 |
19.9 |
18.4 |
18.5 |
C8 |
37.8 |
12.0 |
30.1 |
11.4 |
2.2 |
6.5 |
|
HA 40d |
27.9 |
23.4 |
30.5 |
18.3 |
C9 |
43.6 |
10.5 |
28.0 |
9.5 |
2.2 |
6.3 |
[71] |
CYN/corn straw (70:30 w:w) |
HS 100 d |
16.3 |
13.8 |
24.7 |
28.9 |
5.6 |
10.6 |
C10 |
34.7 |
11.5 |
30.7 |
10.4 |
3.1 |
9.5 |
[88] |
Coffee husks/lettuce residues at (60:40 w:w) |
CT 100 d |
26.9 |
11.9 |
26.4 |
16.6 |
4.3 |
14 |
C11 |
30.2 |
11.3 |
33.6 |
12.0 |
5.3 |
7.7 |
CYN with maize straw/WC (70:30 w:w) |
CT 100 d |
27.6 |
12.1 |
27.3 |
15.0 |
4.2 |
13.9 |
[43] |
SM/ rice straw (4:1 |
PEP with maize straw/WC (70:30 w:w | w:w) |
FS |
24.6 |
57.9 |
7.7 |
9.8 |
) |
CT 100 d |
17.4 |
14.3 |
31.1 |
19.2 |
5.8 |
12.3 |
|
C 40 d |
23.2 |
55.2 |
9.8 |
11.8 |
[68] |
Agricultural crop plants/NH4NO3 (66:34 w:w) |
HA 90 d |
41.63 |
24.89 |
19.31 |
14.16 |
SM/ rice straw (8:1 w:w) |
FS |
28.8 |
50.5 |
7.9 |
Date palm fronds/NH4NO3 (66:34 w:w | 12.8 |
) |
HA 90 d |
36.39 |
29.05 |
23.85 |
|
C 40 d |
25.6 |
48.9 |
10.6 |
15.0 |
10.70 |
Animal waste/NH4NO3 (66:34 w:w) |
HA 90 d |
31.39 |
29.0 |
SM/rice straw/biochar (8:1:1 w:w) |
FS |
24.7 |
40.9 |
24.7 |
9.8 |
25.45 |
14.33 |
[89] |
Tomato R/escarole R/WC/CS (17.5:20.5:60:2) |
CT 105 d |
23.50 |
15.60 |
28.65 |
16.80 |
5.25 |
10.20 |
|
C 40 d |
19.2 |
28.8 |
42.5 |
9.5 |
Tomato R/escarole R/WC/CS (37:11:50:2) |
CT 105 d |
22.55 |
14.95 |
26.65 |
18.25 |
5.90 |
11.75 |
[10] |
COF/fresh grass/mature compost (18:80:2 w:w) |
C 6 d |
33.5 |
15.2 |
23.3 |
14.8 |
3.2 |
10 |
Tomato R/escarole R/WC/CS (50:0:48:2) |
CT 105 d |
23.40 |
14.70 |
26.80 |
17.10 |
6.90 |
11.15 |
[45] |
Solid pig slurry/cotton gin waste (4:3 v:v) |
FS |
13.5 |
5.9 |
Commercial compost from biowaste | 74.9 |
CT 105 d |
26.95 |
12.85 | 3.7 |
0.9 |
1.1 |
32.70 |
10.35 |
2.90 |
14.25 |
|
BT |
17.5 |
8.2 |
62.7 |
5.3 |
1.8 |
4.5 |
[83] |
DOW/COF/pine needles and WT (1:1:1) |
DOM FS |
26.0 |
6.3 |
|
AT |
26.0 |
12.3 |
51.2 |
4.2 |
2.5 |
3.9 |
|
EB |
30.1 |
10.5 |
48.1 |
4.4 |
1.9 |
5.0 |
|
AM |
35.5 |
13.1 |
43.8 |
3.6 |
0.7 |
3.4 |
Solid pig slurry/cotton gin waste (3:4 v:v) |
FS |
19.4 |
9.3 |
71.6 |
0.3 |
0.0 |
0.0 |
|
BT |
13.6 |
7.1 |
71.6 |
5.5 |
1.0 |
1.2 |
|
AT |
18.7 |
4.7 |
61.9 |
7.4 |
3.2 |
4.1 |
|
EB |
26.4 |
11.4 |
53.8 |
5.7 |
4.5 |
6.8 |
|
AM |
34.1 |
12.5 |
44.3 |
3.8 |
1.3 |
4.1 |
Solid pig slurry/cotton gin waste (3:7 v:v) |
FS |
22.9 |
7.4 |
63.6 |
2.3 |
1.1 |
2.7 |
|
BT |
24.9 |
9.3 |
59.1 |
0.9 |
2.0 |
3.9 |
|
AT |
21.0 |
9.3 |
65.5 |
1.1 |
0.9 |
2.2 |
42.1 |
9.5 |
4.9 |
11.1 |
|
DOM 90 d |
30.8 |
7.4 |
27.1 |
13.4 |
|
EB |
18.4 |
8.1 |
69.7 |
2.1 |
1.4 |
0.3 |
|
AM |
21.8 |
9.0 |
58.8 |
2.6 |
2.6 |
5.2 |
[51] |
BM/CM/maize straw/PT (70:30 w:w) |
FS |
15.4 |
10.5 |
58.4 |
8.6 |
3.0 |
4.1 |
|
C 108 d |
18.5 |
11.4 |
48.0 |
12.0 |
3.4 |
6.7 |
+bioplastic (1 wt%) |
C 108 d |
17.6 |
11.1 |
47.9 |
12.3 |
4.0 |
7.1 |
+bioplastic (2 wt%) |
C 108 d |
18.9 |
11.0 |
49.2 |
11.6 |
3.6 |
5.7 |
7.3 |
[49] |
SM/pumice |
FS |
34.6 |
48.5 |
7.3 |
9.7 |
|
C 10 d |
21.5 |
60.4 |
10.5 |
7.7 |
14.0 |
|
C 20 d |
23.6 |
57.7 |
10.9 |
7.7 |
|
C60 d |
26.2 |
48.3 |
12.9 |
12.7 |
CM/pumice |
FS |
14.6 |
23.7 | 64.8 |
12.4 |
8.3 |
28.2 |
|
C 10 d |
9.0 |
70.4 |
12.9 |
7.7 |
|
C 20 d |
10. |
69.2 |
12.7 |
7.7 |
|
C60 d |
11.7 |
66.6 |
13.3 |
8.5 |
ChM/pumice |
FS |
29.5 |
52.3 |
8.2 |
10.1 |
20.3 |
27.8 |
|
HS 120 d |
25.4 |
34.9 |
16.4 |
23.3 |
[79] |
MSW/vegetal wastes (1:1 v:v) |
HA FS |
43.4 |
25.9 |
10.3 |
16.4 |
4.0 |
HA 28 d |
44.7 |
22.1 |
11.0 |
17.9 |
4.3 |
HA 100 d |
42.9 |
20.3 |
11.4 |
17.9 |
7.5 |
|
[61 | C 10 d |
21.5 |
] |
MSW |
HA FS | 66.0 |
32 | 6.4 |
45 | 6.1 |
13 |
10 |
|
C 20 d |
21.7 |
61.6 |
9.3 |
7.4 |
HA 49 d |
48 |
26 |
16 |
10 |
|
C60 d |
26.8 |
52.0 |
10.5 |
10.7 |
[82] |
MSW |
HA 6 d |
38 |
31 |
13 |
5 |
11 |
2 |
HA 19 d |
45 |
23 |
15 |
5 |
11 |
1 |
HA 33 d |
44 |
23 |
16 |
6 |
11 |
1 |
HA 62 d |
42 |
24 |
15 |
6 |
12 |
2 |
HA 105 d |
39 |
25 |
16 |
6 |
12 |
2 |
HA 187 d |
38 |
26 |
17 |
6 |
12 |
3 |
Core-HA 6 d |
34 |
24 |
21 |
8 |
12 |
2 |
Core-HA 19 d |
33 |
23 |
23 |
9 |
11 |
2 |
Core-HA 33 d |
34 |
23 |
23 |
9 |
11 |
1 |
Core-HA 62 d |
38 |
23 |
19 |
7 |
11 |
3 |
Core-HA 105 d |
43 |
21 |
19 |
7 |
10 |
0 |
Core-HA 187 d |
35 |
22 |
20 |
8 |
13 |
3 |
[ |
62 |
DOW/GT/FR (2:1:1) |
DOM FS |
31.8 |
6.2 |
38.5 |
7.9 |
4.3 |
11.4 |
|
DOM 90 d |
34.6 |
7.3 |
25.9 |
13.1 |
4.9 |
14.2 |
GT/COF/spent yeast (1:1:1) |
DOM FS |
30.8 |
5.3 |
41.2 |
6.2 |
2.8 |
13.6 |
|
DOM 90 d |
35.2 |
8.4 |
22.7 |
11.8 |
5.8 |
16.2 |
GT/COF/FR/sewage sludge (4:2:2.5:0.25) |
DOM FS |
30.8 |
6.2 |
38.2 |
8.6 |
4.9 |
11.3 |
|
DO 90d |
33.9 |
7.8 |
25.0 |
13.2 |
5.4 |
14.7 |
[78] |
DOW/GT/vegetal R from tobacco (50:30:20) |
HA 60 d |
28.0 |
11.3 |
32.4 |
16.8 |
11.5 |
HA 90 d |
34.9 |
10.8 |
28.6 |
15.7 |
10.0 |
HA 150 d |
34.5 |
9.3 |
23.1 |
19.8 |
13.4 |
[85] |
OFMSW/GT/foliage R from tobacco (55:30:15) |
CT 120 d |
31.0 |
9.0 |
23.1 |
13.3 |
23.6 |
HoDOM 120 d |
34.6 |
12.6 |
19.5 |
19.3 |
14.0 |
HiDOM 120 d |
30.3 |
9.8 |
36.8 |
9.1 |
14.0 |
[70] |
OvM/straw |
HS FS |
18.6 |
49.7 |
8.2 |
23.5 |
|
HS 120 d |
17.7 |
25.0 |
22.3 |
35.0 |
Mixture of animal manures |
HS FS |
33.7 |
13.8 |
11.8 |
40.7 |
[50] |
Exhausted grape marc/CM (76:24 w:w) |
FS |
30.7 |
17.0 |
39.5 |
3.3 |
3.5 |
6.1 |
|
C 28 d |
36.4 |
15.9 |
31.2 |
5.7 |
3.7 |
7.3 |
|
C105 d |
37.9 |
16.1 |
28.9 |
6.3 |
3.9 |
6.9 |
|
C 168 d |
37.3 |
14.3 |
22.4 |
7.1 |
4.8 |
14.2 |
Grape marc/CM (72:28 w:w) |
FS |
33.6 |
15.3 |
37.1 |
2.9 |
3.7 |
7.4 |
|
C 28 d |
34.3 |
13.7 |
37.3 |
3.6 |
3.6 |
7.5 |
|
C105 d |
33.3 |
14.8 |
38.6 |
3.8 |
3.0 |
6.6 |
|
C 168 d |
34.9 |
15.2 |
34.4 |
3.3 |
4.0 |
8.2 |
Exhausted grape marc/PM (67:33 w:w) |
FS |
30.8 |
14.2 |
41.0 |
3.5 |
3.5 |
7.0 |
|
C 28 d |
34.4 |
14.6 |
35.4 |
3.2 |
4.0 |
8.5 |
|
C105 d |
33.9 |
15.5 |
35.7 |
3.7 |
3.9 |
7.5 |
|
C 168 d |
34.3 |
15.5 |
31.5 |
3.4 |
5.0 |
10.2 |
[42] |
CM |
CC |
|
HS 120 d |
30.4 |
24.0 |
9.6 |
36.0 |
Solid olive mill wastes |
HS FS |
23.2 |
56.4 |
11.2 |
9.2 |
|
HS 120 d |
18.2 |
7.6 |
48.8 |
8.9 |
5.0 |
11.6 |
Broiler litter |
CC |
17.9 |
9.1 |
48 |
8.0 |
5.2 |
11.7 |
Green waste |
CC |
22.4 |
10.7 |
40.4 |
8.2 |
6.3 |
12.0 |
Nitro-humus |
CC |
19.6 |
8.8 |
43 |
9.6 |
6.7 |
12.4 |
MSW |
CC |
23.0 |
7.6 |
48.7 |
7.3 |
3.6 |
9.8 |
[56] |
Rice husk/rice bran/BEM/molasses |
FS |
2.15 |
25.8 |
67.4 |
2.98 |
0.99 |
22.2 |
29.3 |
C 13 d |
1.98 |
25.6 |
68.9 |
3.07 |
0.51 |
19.7 |
C 34 d |
0.66 |
25.6 |
70.8 |
2.98 |
- |
C 53 d |
1.10 |
22.6 |
73.1 |
3.29 |
- |
C 61 d |
1.03 |
24.0 |
71.9 |
3.09 |
- |
C 116 d |
0.88 |
25.7 |
69.9 |
2.63 |
0.88 |
[55] |
DOW/plant trimming/vegetal R (50:40:10 w:w) |
C 60 d |
37.6 |
50.8 |
7.2 |
4.3 |
C 90 d |
30.6 |
56.1 |
7.3 |
6.1 |
C 150 d |
45.3 |
37.6 |
9.6 |
7.4 |
[46] |
CM/rice straw |
FS |
14.9 |
54.9 |
20.3 |
10.0 |
28.8 |
Solid wastes of wineries |
HS FS |
3.5 |
46.9 |
1.5 |
48.1 |
|
HS 120 d |
21.6 |
13.1 |
26.8 |
38.5 |
Domestic wastes |
HS FS |
[81] |
OFMSW |
HA FS |
37.20 |
34.34 |
16.28 |
12.23 |
C 60 d |
17.4 |
57.4 |
20.9 |
10.6 |
C 120 d |
HA C |
30.07 |
34.71 |
22.67 |
12.58 |
17.4 |
48.6 |
18.6 |
9.9 |
C 240 d |
15.2 |
34.1 |
16.1 |
9.2 |
C 365 d |
13.9 |
25.7 |
12.4 |
6.5 |
C 548 d |
12.8 |
22.8 |
11.3 |
6.6 |
FS |
13.5 |
56.7 |
20.1 |
9.7 |
C 148 d |
15.2 |
39.6 |
18.7 |
10.0 |
FS |
15.2 |
56.4 |
18.8 |
9.6 |
C 60 d |
13.4 |
47.5 |
16.5 |
8.4 |
C 120 d |
12.6 |
42.0 |
17.5 |
8.5 |
C 240 d |
12.1 |
37.2 |
15.9 |
8.1 |
C 365 d |
12.6 |
35.6 |
15.3 |
7.7 |
[44] |
SM/wheat straw (95:5 w:w) |
FS |
27.2 |
55.6 |
9.2 |
8.0 |
C 7 d |
18.6 |
66.1 |
9.8 |
5.5 |
C 14 d |
15.2 |
65.3 |
12.2 |
7.3 |
C 21 d |
16.8 |
65.2 |
11.5 |
6.5 |
C 28 d |
14.7 |
63.3 |
13.6 |
8.3 |
[61] |
MSW (composted in spring) |
FS |
15.8 |
59.5 |
14.9 |
7.9 |
|
C 28 d |
17.7 |
59.2 |
13.6 |
7.4 |
|
C 42 d |
17.5 |
55.5 |
16.2 |
7.2 |
|
C 49 d |
17.3 |
55.5 |
17.7 |
5.4 |
MSW (composted in summer) |
FS |
16.2 |
60.4 |
12.1 |
7.8 |
|
C 28 d |
16.8 |
60.2 |
13.9 |
6.9 |
|
C 42 d |
18.0 |
56.1 |
15.3 |
6.8 |
|
C 49 d |
18.2 |
56.9 |
15.8 |
6.0 |
[60] |
Kitchen waste/garden waste |
C1 |
28.4 |
45.6 |
7.4 |
4.6 |
14.0 |
C2 |
25.4 |
48.6 |
9.8 |
4.8 |
11.4 |
C3 |
30.3 |
32.5 |
11.1 |
6.3 |
19.8 |
C4 |
32.4 |
38.2 |
7.9 |
4.9 |
16.6 |
C5 |
19.2 |
53.0 |
12.8 |
8.2 |
6.8 |
C6 |
25.5 |
40.8 |
12.6 |
6.6 |
14.5 |
C7 |
27.4 |
42.8 |
11.3 |
6.3 |
12.2 |
C8 |
26.7 |
42.6 |
9.0 |
7.9 |
13.8 |
C9 |
14.1 |
43.6 |
8.1 |
12.0 |
] |
MSW |
FS |
26.9 |
47.9 |
11.6 |
4.3 |
8.3 |
C 34 d |
25.5 |
52.1 |
10.5 |
3.6 |
8.2 |
C 76 d |
24.7 |
46.5 |
13.6 |
4.9 |
10.3 |
C 90 d |
23.6 |
42.4 |
19.0 |
6.6 |
11.4 |
C132 d |
23.6 |
40.4 |
16.9 |
7.6 |
11.4 |
[59] |
Grape skin |
FS |
8.7 |
53.4 |
17.5 |
18.7 |
|
C 160 d |
10.9 |
51.8 |
18.9 |
17.0 |
Grape seeds |
FS |
25.0 |
41.3 |
13.1 |
18.7 |
|
C 160 d |
21.7 |
38.4 |
15.7 |
22.3 |
Grape skin and seeds |
FS |
16.2 |
49.7 |
13.2 |
18.8 |
|
C 160 d |
18.6 |
43.7 |
15.9 |
20.3 |